Compositions involving Cr2 --O3 --V2 O3 --TiO2

ABSTRACT

The present invention pertains to novel solid solutions involving Cr 2  O 3 , V 2  O 3  and TiO 2  and the method for their preparation. The solid compositions involving Cr 2  O 3 , V 2  O 3  and TiO 2  fall within the shaded area of a polygon in a ternary composition diagram of Cr 2  O 3 , V 2  O 3  and TiO 2  as shown in the drawing herein e.g., FIG. 1. The composition may be used as an oxidation catalyst or in the manufacture of high temperature refractories.

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

This invention relates to compositions involving Cr₂ O₃ --V₂ O₃ --TiO₂.

SUMMARY OF THE INVENTION

The present invention pertains to novel solid solutions involving Cr₂O₃, V₂ O₃ and TiO₂ and the method for their preparation. The solidcompositions involving Cr₂ O₃, V₂ O₃ and TiO₂ fall within the shadedarea of a polygon in a ternary composition diagram of Cr₂ O₃, V₂ O₃ andTiO₂ as shown in the drawing herein e.g. FIG. 1. The polygon has thevertices and corresponding coordinates in weight percent as shown in thefollowing Table I.

                  TABLE I                                                         ______________________________________                                                Coordinates (wt %)                                                    Vertices  Cr.sub.2 O.sub.3                                                                            V.sub.2 O.sub.3                                                                       TiO.sub.2                                     ______________________________________                                        A         45            55       0                                            B         45            35      20                                            C         10            35      55                                            D          2            43      55                                            F          2            98       0                                            ______________________________________                                    

The compositions involving Cr₂ O₃, V₂ O₃ and TiO₂ are depicted by theshaded area circumscribed by ABCDF as shown in FIG. 1. These novel solidsolutions involving C₂ O₃, V₂ O₃, and TiO₂ are made by the processinvolving the steps of:

(1) heating V₂ O₅ powder having a particle size of less than about 50microns in an atmosphere in which the partial pressure of oxygen is inthe range of 10⁻⁸ to 10⁻¹⁰ atmosphere while gradually increasing thetemperature over a temperature range of about 600° C. to 1300° C., andholding the temperature at about 1300° C. for a period to ensurecomplete reduction of all vanadium to V³⁺ ;

(2) heating TiO₂ and Cr₂ O₃ powders each having a particle size of lessthan about 50 microns for a period of about 10 to 14 hrs. at atemperature in the range of about 600° C. to 800° C. for TiO₂ and about1000° C. to 1200° C. for Cr₂ O₃ ;

(3) thoroughly grinding together about 35 to 98 wt. % of V₂ O₃ from (1),with about 0 to 55 wt. % of TiO₂ and about 2 to 45 wt. % of Cr₂ O₃ from(2) to produce a mixture having a grain size of less than about 50microns,

(4) pelletizing the mixture from (3) at a pressure of about 5,000 psi;and

(5) heating and reacting together the pellets from (4) at a temperaturein the range of about 1100° C. to 1800° C. for a period in the range ofabout 1/2 to 48 hrs., in an atmosphere in which the partial pressure ofoxygen is in the range of 10⁻¹⁰ to 10⁻⁵ atmosphere to produce saidcompositions involving Cr₂ O₃, V₂ O₃ and TiO₂.

In one embodiment, the pellets from step (5) are cooled to ambienttemperature while at substantially the same partial pressure of oxygenas in step (5). Preferably, to prevent undue oxidation and moisturepickup, the cooled pellets are stored in a sealed container.

BRIEF DESCRIPTION OF THE DRAWING

The drawing e.g. FIG. 1 depicts a ternary composition diagram showing apolygon shaped shaded area circumscribed by ABCDF within which usefulcompositions involving Cr₂ O₃ --V₂ O₃ --TiO₂ are found.

DESCRIPTION OF THE INVENTION

New solid solutions have been synthesized by the subject invention inwhich the nature and extent of the formation of solid solutionsinvolving Cr₂ O₃, V₂ O₃ and TiO₂ have been characterized. This work hasled to synthesizing new phases in which vanadium in several oxidationstates are accommodated such as to render crystalline phasesthermodynamically stable over a wide range of oxygen pressures atelevated temperatures.

The newly synthesized solid compositions involving Cr₂ O₃ --V₂ O₃ --TiO₂are shown in the enclosed figure (drawing) as circumscribed by thepolygon shaped shaded area ABCDF in the ternary composition diagram. Theoxidation states of vanadium in the solid solutions are mainly +3 and+4.

The polygon shaped shaded area ABCDF has the following vertices andcorresponding coordinates in weight percent:

    ______________________________________                                                Coordinates (wt %)                                                    Vertices  Cr.sub.2 O.sub.3                                                                            V.sub.2 O.sub.3                                                                       TiO.sub.2                                     ______________________________________                                        A         45            55       0                                            B         45            35      20                                            C         10            35      55                                            D          2            43      55                                            F          2            98       0                                            ______________________________________                                    

A typical newly synthesized material comprising a sesquioxide phasehaving the formula Cr₀.40 V₁.60 O₃.0, and a Me₂ TiO₅ phase (where Me=Cror V) having the formula Cr₀.40 V₁.60 Ti₁.00 O₅.0 ; as illustrated bypoint G in the drawing and having the following coordinates in wt. %:Cr₂ O₃ 15, V₂ O₃ 60, and TiO₂ 25.

The subject compositions made from Cr₂ O₃, V₂ O₃ and TiO₂ aresynthesized in the following manner. The identity of the reactionproduct, solid solutions involving Cr₂ O₃ --V₂ O₃ --TiO₂, may beconfirmed by X-ray diffraction analysis.

First, V₂ O₃ is prepared by heating commercially availableanalytical-grade V₂ O₅ having a particle size of less than about 50microns in a vertical tube furnace in an atmosphere of carefullyselected oxygen pressure within the stability range of V₂ O₃ e.g. in therange of 10⁻⁸ to 10⁻¹⁰ atmospheres. This is accomplished by using a gasmixture of high-purity e.g. 99.9 mole % or more CO₂ and H₂ or CO₂ and COor H₂ O and H₂ in controlled proportions. The CO₂ /H₂, CO₂ /CO or H₂O/H₂ ratio by volume is in the range of 10/1 to 1/1. The relatively lowmelting point of the starting vanadium oxide (V₂ O₅) e.g. about 690° C.,necessitates heating the oxide slowly. Starting at a temperature ofabout 600° C., the temperature is gradually increased over a period ofabout 12 to 24 hrs. to a final temperature of about 1300° C. At atemperature of about 1300° C. the vanadium oxide is held at least about24 hrs e.g. about 24 to 30 hrs., to ensure complete reduction of allvanadium to V³⁺.

Preheated analytical-grade oxides having a particle size of less thanabout 50 microns are used as starting materials for the other componentsof the solid solutions to be synthesized. For example, TiO₂ is heatedfor about 10 to 14 hrs. at a temperature in the range of about 600° C.to 800° C. and Cr₂ O₃ is separately heated for about 10 to 14 hrs. at atemperature in the range of about 1000° C. to 1200° C. prior to beingused in preparation of the final mixtures. The oxides are therebydemoisturized. They may be then cooled to ambient conditions.

The mixtures of the three oxide components are thoroughly mechanicallyground together under acetone in an agate mortar to ensure thoroughmixing and a sufficiently small grain size e.g. less than 50 microns.For example, about 35 to 98 wt. % of V₂ O₃ is ground together with about0 to 55 wt. % of TiO₂ and about 2 to 45 wt. % of Cr₂ O₃ to produce amixture having a grain size of less than about 50 microns. Completeformation of the desired compounds in the succeeding heat treatment isthereby promoted. Next, the oxide mixtures are pelletized at a pressureof about 5,000 psi or higher. The pellets may have any conventional sizee.g. 1/16" to 1". The pellets are then heated and reacted together at atemperature in the range of about 1100° C. to 1800° C., such as about1200° C. to 1300° C., for a period in the range of about 1/2 to 48 hrs.,such as about 1/2 to 2 hrs. or 12 to 48 hrs. (depending on the natureand solidus temperature of the phase to be synthesized) in a verticaltube furnace with carefully controlled oxygen pressures, in the range of10⁻¹⁰ to 10⁻⁵ atmosphere. In the manner described previously forpreparing V₂ O₃, the pellets are heated in a furnace atmosphere providedby a gas mixture of CO₂ and H₂ or CO₂ and CO or H₂ O and Hz in variousdesired volumetric mixing ratios. For example, the volumetric ratio CO₂/H₂, CO₂ /CO, or H₂ O/H₂ is typically in the range of about 10/1 to 1/1.These selected ratios are kept constant for the duration of thesynthesis by use of a differential manometer. By this method the oxygenpressure at the specified temperature can be controlled to better than±1%. The thermodynamic data for the water-gas shift reaction (CO₂ +H₂=CO+H₂ O), on which the calculations were based, are known withextremely high accuracy (better than 0.1%). Hence, the method usedherein ensures reliable accurate control of the oxidation state ofvanadium during the synthesis. This is extremely important foroptimization of the properties of the finished product.

At the time of the high temperature reaction in the range of about 1100°C. to 1800° C., all of the oxide pellets may be in the solid state or atleast one, two or three of the oxide constituents may be in the moltenstate. At the reaction conditions prevailing in the subject process,solid solutions may be made by solid-state reactions considerably belowtemperatures at which a liquid phase is present. However, the presenceof a liquid phase or a solid-liquid phase improves the kinetics of thereaction.

The individual oxide components are heated to a sufficiently hightemperature to expel absorbed or adsorbed water. Well defined startingmaterials for accurately weighing up mixtures are thereby produced. Aspreviously described, V₂ O₅ was heated slowly to a temperature of about1300° C. at controlled oxygen pressures in order to decompose the V₂ O₅slowly to V₂ O₃. By this means, violent reactions are avoided at thehighest temperatures, and the vanadium is produced in the desiredoxidation state V³⁺.

The oxide mixtures were heated at temperatures in the range of about1100° C.-1800° C. in order to promote reaction among the oxidecomponents to the desired finished products consisting mainly of one ormore (solid-solution) phases. In one embodiment, the mixture of solidparticles was heated to a temperature below the solidus, for example toabout 1200° C. The phase assemblage of the final product was producedentirely by solid state reaction. Under such conditions, the crystalswere relatively small, typically, of about 0.5-3.0 microns. In anotherembodiment, the mixtures were heated to a sufficiently high temperaturee.g. about 1750° C. to produce partial or complete melting. This speedsup the reaction and produces (solid solution) phases (crystals) oflarger size, typically in the range of about 2-100 microns. Afterheating the mixtures at this high temperature for a period of time, suchas 1/2-2 hrs., the composition is cooled to ambient conditions. Forexample, the composition may be cooled slowly (over a period of 1/2-1hr) to about 1200° C. From this temperature, the composition may becooled rapidly (quenched) to room temperature. During these runs theoxygen pressure of the gas phase was controlled by using gas mixtures ofCO₂ and H₂, CO₂ and CO, or H₂ O and H₂ with volumetric ratios CO₂ /H₂,CO₂ /CO or H₂ O/H₂ in the range of about 10/1-1/1. These selected ratiosare kept constant for the duration of the synthesis, for example, by useof a differential manometer.

In addition to oxygen pressure, one other parameter influencing theoxidation state of vanadium in oxide phases has been utilized insynthesizing the new phases. This is the provision of host structureswhich incorporate vanadium in one (or more) valence state(s) in strongpreference to other valence states. In the present case, the extensiveternary solid-solution phases (spinel, pseudobrookite, and mixturesthereof) in the system Cr₂ O₃ --V₂ O₃ --TiO₂ serve this purpose. Inthese solid solutions, the vanadium is present partly in the trivalentstate and partly in the tetravalent state, the preferential substitutionof V⁴⁺ for Ti⁴⁺.

The sesquioxide solid-solution phase of corundum-type structure iscomplete between the two end members Cr₂ O₃ and V₂ O₃, and the Me₂ TiO₅phase of Cr₂ TiO₅ structure is complete between the two end members Cr₂TiO₅ and V₂ TiO₅.

The pellets of the composition involving Cr₂ O₃ --V₂ O₃ --TiO₂ may beused as an oxidation catalyst, offering improved activity and yields andgreater stability over a wider temperature range. For example, thecomposition is stable at a temperature which is about 800° C higher thanthat which is offered by typical oxidation catalysts. Otherwise,conventional conditions for oxidation reactions may be used. As anoxidation catalyst, the subject pellets may be used in the conversion ofo-xylene to phthalic anhydride, butane to maleic anhydride, or alcoholsto aldehydes or organic acids.

As a high temperature refractory or as an ingredient in a hightemperature refractory material for lining a gasifier for the partialoxidation of ash-containing liquid hydrocarbonaceous and solidcarbonaceous fuels, the subject material would have a long life,withstanding attack from V₂ O₅. For example, a thermal refractory forlining the reaction zone of a partial oxidation gas generator maycomprise the previously described composition involving Cr₂ O₃ --V₂ O₃--TiO₂ in the amount of about 1 to 25 wt. %, and the remainder of therefractory e.g. about 75 to 99 wt. % involving oxides with a cationicportion that is selected from the group consisting of Fe, Mg, Al, Mn, Siand mixtures thereof. The partial oxidation reactor operates in areducing atmosphere and at a temperature in the range of about 1700° F.to 3000° F.

The subject solid composition involving Cr₂ O₃ --V₂ O₃ --TiO₂ may alsobe used as an additive. About 0.01 to 0.2 wt. % (basis weight of ash inthe fuel fed to the gas generator) of additive may be introduced intothe refractory lined partial oxidation gas generator to stabilize saidrefractory.

Various modifications of the invention as herein before set forth may bemade without departing from the spirit and scope thereof, and therefore,only such limitations should be made as are indicated in the appendedclaims.

We claim:
 1. A method of preparing a composition from Cr₂ O₃, V₂ O₃ andTiO₂ wherein said composition falls within the shaded area circumscribedby ABCDF as shown in the disclosed FIGURE, and wherein said methodcomprises the steps of:(1) heating V₂ O₅ powder having a particle sizeof less than about 50 microns in an atmosphere in which the partialpressure of oxygen is in the range of 10⁻⁸ to 10⁻¹⁰ atmospheres whilestarting at a temperature of 600° C. and gradually increasing thetemperature over a period in the range of about 12 to 24 hours to about1300° C. and holding the temperature at about 1300° C. for a period toensure complete reduction of all vanadium to V³⁺ ; (2) separatelyheating TiO₂ and Cr₂ O₃ powders each having a particle size of less thanabout 50 microns for a period of about 10 to 14 hrs at a temperature inthe range of about 600° C. to 800° C. for TiO₂ and about 1000° C. to1200° C. for Cr₂ O₃ ; (3) thoroughly grinding together about 35 to 98wt. % of V₂ O₃ from (1), with about 0 to 55 wt. % of TiO₂ and about 2 to45 wt. % of Cr₂ O₃ from (2) to produce a mixture having a grain size ofless than about 50 microns; (4) pelletizing the mixture from (3) at apressure of about 5,000 psi; and (5) heating and reacting together thepellets from (4) at a temperature in the range of about 1100° C. to1800° C. for a period in the range of about 1/2 to 48 hrs in anatmosphere in which the partial pressure of oxygen is in the range of10⁻¹⁰ to 10⁻⁵ atmosphere.
 2. The method of claim 1 where in said FIGUREthe amounts of Cr₂ O₃, V₂ O₃ and TiO₂ are characterized as shown in theTable below;

    ______________________________________                                                Coordinates (wt %)                                                    Vertices  Cr.sub.2 O.sub.3                                                                            V.sub.2 O.sub.3                                                                       TiO.sub.2                                     ______________________________________                                        A         45            55       0                                            B         45            35      20                                            C         10            35      55                                            D          2            43      55                                            F          2            98       0                                            ______________________________________                                    


3. The method of claim 1 which further comprises the steps of coolingthe pellets of (5) to ambient temperature, while at substantially thesame partial pressure of oxygen as in (5); and storing the cooledpellets in a sealed container.
 4. The method of claim 1 wherein saidcomposition comprising Cr₂ O₃, V₂ O₃ and TiO₂ is a solid solution. 5.The method of claim 1 wherein at the time of reaction in (5) at leastone, two or three of the oxide constituents are in the molten state. 6.The method of claim 1 where in step (1) said V₂ O₅ powder is heated inan atmosphere comprising a gas mixture of CO₂ and H₂ having a volumeratio of CO₂ /H₂ in the range of about 10/1 to 1/1.
 7. The method ofclaim 1 where in step (5) said pellets are heated in an atmospherecomprising a gas mixture of CO₂ and H₂ having a volume ratio of CO₂ /H₂in the range of about 10/1 to 1/1.
 8. The method of claim 1 where insteps (1) and (5) said materials are heated in an atmosphere comprisinga gas mixture of CO₂ and CO or H₂ O and H₂ having volumetric ratios CO₂/CO or H₂ O/H₂ in the range of about 10/1 to 1/1.
 9. The method of claim1 wherein said composition comprises a susquioxide phase having theformula Cr₀.40 V₁.60 O₃.0, and a phase having the formula Cr₀.40 V₁.60Ti₁.00 O₅.0 ; as illustrated by point G in said disclosed FIGURE andhaving the following coordinates in wt. % Cr₂ O₃ 15, V₂ O₃ 60, and TiO₂25.
 10. The method of claim 1 wherein said composition has a structureselected from the group consisting of spinel, pseudobrookite, andmixtures thereof.
 11. Composition produced from Cr₂ O₃, V₂ O₃ and TiO₂,wherein said composition is a solid solution and falls within the shadedarea circumscribed by ABCDF as shown in the disclosed FIGURE wherein theamounts of Cr₂ O₃, V₂ O₃ and TiO₂ are characterized as shown in thetable below:

    ______________________________________                                                Coordinates (Wt %)                                                    Vertices  Cr.sub.2 O.sub.3                                                                            V.sub.2 O.sub.3                                                                       TiO.sub.2                                     ______________________________________                                        A         45            55       0                                            B         45            35      20                                            C         10            35      55                                            D          2            43      55                                            F          2            98      
 0.                                           ______________________________________                                    


12. A composition as provided in claim 11 comprising a susquioxide phasehaving the formula Cr₀.40 V₁.60 O₃.0, and a having the formula Cr₀.40V₁.60 Ti₁.00 O₅.0 ; as illustrated by point G in said disclosed FIGUREand having the following coordinates in wt. % Cr₂ O₃ 15, V₂ O₃ 60, andTiO₂
 25. 13. Composition produced from Cr₂ O₃, V₂ O₃, and TiO₂ and inwhich the vanadium is present in the trivalent or tetravalent state, andthe structure is selected from the group consisting of spinel,pseudobrookite, and mixtures thereof; wherein said composition ischaracterized by its ability to catalyze oxidation reactions and saidcomposition falls within the shaded area circumscribed by ABCDF as shownin the disclosed FIGURE wherein the amounts of Cr₂ O₃, V₂ O₃ and TiO₂are characterized as shown in the table below:

    ______________________________________                                                Coordinates (Wt %)                                                    Vertices  Cr.sub.2 O.sub.3                                                                            V.sub.2 O.sub.3                                                                       TiO.sub.2                                     ______________________________________                                        A         45            55       0                                            B         45            35      20                                            C         10            35      55                                            D          2            43      55                                            F          2            98      
 0.                                           ______________________________________                                    


14. Thermal refractory composition comprising, ( 1) a solid solution and(2) at least one oxide having a cationic portion selected from the groupconsisting of Fe, Mg, Al, Mn, Si, and mixtures thereof; wherein saidsolid solution is produced from Cr₂ O₃, V₂ O₃ and TiO₂ and has acomposition that falls within the shaded area circumscribed by ABCDF asshown in the disclosed FIGURE wherein the amounts of Cr₂ O₃, V₂ O₃ andTiO₂ are characterized as shown in the table below:

    ______________________________________                                                Coordinates (Wt %)                                                    Vertices  Cr.sub.2 O.sub.3                                                                            V.sub.2 O.sub.3                                                                       TiO.sub.2                                     ______________________________________                                        A         45            55       0                                            B         45            35      20                                            C         10            35      55                                            D          2            43      55                                            F          2            98      
 0.                                           ______________________________________                                    